Milling machines for processing the ground are frequently used in order to break up and/or loosen the ground, to mix materials such as bonding agents (especially lime or cement) into the ground, add or distribute fluids (especially water), etc. In view of the specific applications, generic milling apparatuses are frequently classified as one of the following types of construction machines: milling machines, especially cold milling machines, stabilizers and recyclers. Cold milling machines are used for milling off road surfaces and ground coverings, while stabilizers are used for stabilizing non-supporting grounds and recyclers for repairing pavements in need of repair, wherein it will be appreciated that there can be some overlap concerning the spectrum of applications.
A generic milling machine for milling off and/or breaking up the ground and/or for mixing additives into the ground material usually comprises a milling rotor which is arranged horizontally and transversely to the working direction of the milling apparatus and which is rotatable about its cylinder axis. The milling rotor usually comprises a cylindrical roller body on which a plurality of suitable processing tools such as cutters is arranged. The milling rotor is arranged to be lowerable for processing the ground and for regulating the milling depth in the ground. In order to shield the milling rotor to the outside during working operation, the milling apparatus further comprises a rotor housing or rotor hood. The rotor hood is open towards the ground so that the milling rotor of the milling apparatus can come into contact with the ground to be processed. The hood is provided with a curved configuration for this purpose, wherein curvature shapes with corners and edges are included in the meaning of the word hood here. It is essential for the function of the rotor hood that it represents a kind of spatial limitation upwards and laterally, i.e., above the ground surface, for the milling rotor. Such a rotor hood is known from DE 20 2008 016 935 U1, for example.
Specifically, the rotor hood comprises a front hood part, a rear hood part and two lateral hood parts, which together form the rotor housing. According to its definition, the front hood part is the portion of the rotor hood which, in the working direction of the milling apparatus, lies in front of the longitudinal axis of the roller body of the milling rotor. The rear hood part is accordingly the portion of the rotor hood which lies behind the rotational axis of the milling rotor in the working direction, respectively when the milling rotor is in its maximally raised-up position in relation to the rotor hood, as the rotor hood is configured to be adjustable relative to the milling rotor. The lateral hood parts close off the space enclosed by the rotor hood to the sides and on the face side relative to the rotational axis and in the axial direction of the milling rotor. It will be appreciated that the front and the rear hood part and the two lateral hood parts can vary with respect to their specific shape. The importance of the shape of the rotor hood is the protective function achieved by the same in order to prevent the ejection of loosened and broken-up ground material during the working process. Another important function of the rotor hood is to limit the processing space around the milling rotor in order to effectively enable, e.g., thorough mixing and/or a milling operations. The rotor hood is adapted so that it extends downwards approximately to the level of the ground to be processed when in working operation in order to enable the most comprehensive and complete enclosure of the milling rotor outwards.
At the same time, the available free space between the milling rotor has an essential influence on the maximum output of the milling apparatus. The deeper the milling apparatus engages in the ground to be processed, the more free space is required between the milling rotor and the inside of the rotor hood facing the milling rotor in order to ensure the required removal of the milled ground material. For mixing processes, such as, e.g., for the admixture of a bonding agent into the ground, it is principally advantageous if the rotor hood encloses the milling rotor in a comparatively tight manner especially in the region to the rear in the working direction (the region behind the working roller in the working direction) and guides milled or ground material towards the milling rotor. Material that is milled in the front region—e.g., during a counter-rotating operation during which the processing tools of the working roller move in the area of engagement with the ground in the opposite direction of the motion of the ground relative to the working roller—is not deposited behind the milling rotor in the working direction in the case of a rotor hood that is tightly guided in the rear region but is conveyed to a large part again in the direction of rotation. As a result, this already loose ground material can be processed again by the working roller and thus be broken up and mixed even better. However, the improved mixing and milling operations have a negative effect on intake capacity for further ground material to be processed so that there is a comparatively lower milling speed at a fixed comparative milling depth and thus a lower efficiency of the milling apparatus with respect to the working speed.
However, if the rotor hood is configured so that especially the free space to the inside wall of the rotor hood behind the milling rotor in the working direction of the milling apparatus is comparatively large, the milled material will be deposited or thrown to a large extent to the rear or behind the milling rotor in the working direction and thus not transported back to the front of the milling rotor in the rotational direction. As a result, nearly the entire rotor output can be used for milling new material, thus enabling a very high milling speed at the determined comparative milling depth and a particularly high efficiency of the machine. However, the quality of the mixture and the extent and homogeneity of the milling will be adversely affected.
In addition to the curved housing for regulating an outlet opening in the rotor hood, the rotor hood of DE 20 2008 016 935 U1 further comprises a flap which is arranged on the rear housing part of the rotor hood in relation to the direction of travel. The direction of travel specifically indicates the direction in which the rotor hood or a milling apparatus is moved over the ground to be processed during working operation. An adjustable stripping lip is further arranged on a rear edge of the flap. The stripping lip is used to smooth the milled material behind the rotor hood. Alternatively, stripping apparatuses are also known which are configured in a fixed manner with respect to the rotor hood. In the simplest of cases, such stripping apparatuses can be a bottom edge of the rotor housing. Due to the fact that the stripping device is arranged on the flap in a pivotable manner, the angular position of the stripping device can be kept constant with respect to the ground at different positions of the flap.
The requirements placed on the milling machine with regard to milling, mixing and milling speed can vary significantly depending on the target objectives and depending on the properties of the ground material to be processed. The main focus can be, e.g., the maintenance of the most homogeneous milling or an especially constant distribution or mixture of the ground material to be processed with one or several additives. In other cases, the quickest possible processing of the ground may be advantageous. In addition, it is frequently desirable to enable better control of the ratio between rapid processing of the ground and efficient milling/mixing, e.g., in order to enable a more effective response to changing ground conditions during working operation.